For many years, curable epoxy resins have been used as components in coating compositions. However, the properties of coatings produced using aqueous epoxy resin dispersions have long been considered inferior to those of coatings in which the resin is used in the form of a solution in an organic solvent. This was mainly attributed to the fact that the emulsifiers used, for example nonylphenol ethoxylates, migrate to the surface of the film where they adversely affect its properties. One way of solving this problem is to use so-called reactive emulsifiers which, where the epoxy resin is crosslinked with a diamine or polyamine or other hardener, react with the hardener and thus become part of the coating. Aqueous dispersions of special reactive emulsifiers are known from the prior art.
U.S. Pat. No. 4,315,044 describes a stable epoxy resin dispersion containing (1) an aqueous medium and (2) between 50 and 70% by weight of a self-emulsifiable epoxy resin which is the addition product of (a) 40 to 90% by weight of diglycidyl ethers of a dihydric phenol, (b) 5 to 35% by weight of a dihydric phenol and (c) 2 to 15% by weight of the diglycidyl ether of a polyoxyalkylene glycol and in which the molecular weight of the epoxy resin is between 500 and 20,000.
U.S. Pat. No. 4,608,406 describes a stable epoxy dispersion containing (1) an aqueous medium and (2) between 50 and 70% by weight of a self-emulsifiable epoxy resin with a molecular weight of 1,000 to 20,000 which is the addition product of (a) 40 to 90% by weight of diglycidyl ethers of a dihydric phenol, (b) 5 to 35% by weight of a dihydric phenol, (c) 2 to 15% by weight of the diglycidyl ether of a polyoxyalkylene glycol and (d) 2 to 15% by weight of an alkyl phenol/formaldehyde/novolak resin.
EP-B-272 595 and DE-A-36 43 751 describe a process for the production and use of stable aqueous epoxy resin dispersions consisting of a) 50 to 80% by weight of an epoxy compound containing at least two epoxy groups per molecule and having an epoxy equivalent weight of 100 to 2,000, b) 35 to 17% by weight of an aromatic polyol and c) 15 to 3% by weight of a condensation product of an aliphatic polyol with a molecular weight (Mw) of 200 to 20,000 and an epoxy compound containing at least two epoxy groups per molecule and having an epoxy equivalent weight of 100 to 2,000, the equivalent ratio of the OH groups to the epoxy groups being from 1:0.85 to 1:3.5 and the epoxy equivalent weight of this condensation product being from 200 to at least 50,000.
WO 95/18165 (Henkel Corp.) describes a self-dispersible curable epoxy resin obtainable by reacting an epoxy resin (a) with a polyoxyalkylene amine (b) with a molecular weight of 3,000 to 15,000. The components mentioned are used in a ratio of (b) to (a) of 0.001:1.0 to 0.060:1.0 equivalent.
WO 96/20970 (Henkel Corp.) describes a self-dispersible curable epoxy resin obtainable by reacting (a) 1.0 equivalent of epoxy resin, (b) 0.01 to 1.0 equivalent of a polyhydric phenol and (c) 0.005 to 0.5 equivalent of an amine/epoxy adduct. The amine/epoxy adduct is a reaction product of 1.0 equivalent of a polyepoxide and 0.3 to 0.9 equivalent of a polyoxyalkylene diamine.
EP-A-747 413 describes a self-emulsifiable epoxy resin (A) obtainable from (A-1) 50 to 95% by weight of one or more epoxy compound(s) containing at least two epoxy groups per molecule and having an epoxy group content of 300 to 11,200 mmoles/kg, (A-2) 5 to 50% by weight of an aromatic polyol, (A-3) 0 to 25% of modifying compounds containing at least two epoxy-reactive groups, (A4) 5 to 35% of a condensation productxe2x80x94acting as emulsifierxe2x80x94of (A4-a) an aliphatic polyol with a weight average molecular weight Mw of 200 to 20,000 g/mole and (A-4-b) an epoxy compound containing at least two epoxy groups per molecule and having an epoxy group content of 500 to 10,000 mmoles/kg, the ratio of the number of OH groups to the number of EP groups being from 1:2 to 1:10 and the epoxy group content of the condensation products (A4) being from 100 to 6,700 mmoles/kg.
The present invention relates generally to self-dispersing, hardenable epoxy resins, the epoxy resins based on xcex1,xcex2-unsaturated carboxylic acid esters, processes for their production, aqueous dispersions containing such epoxy resins, and to their use in coating solid substrates.
The problem addressed by the present invention was to provide self-dispersible curable epoxy resins. The expression xe2x80x9cself-dispersiblexe2x80x9d in the context of the present invention means that the epoxy resins can be dispersed or emulsified spontaneously in aqueous medium without the use of additional additives, such as emulsifying or dispersing additives. In other words, the epoxy resins to be developed are those which would be capable of self-dispersion and/or self-emulsification in water. In the interests of simplicity, the term xe2x80x9cself-dispersingxe2x80x9d is used for this property throughout the present specification. Another problem addressed by the invention was to provide aqueous dispersions of self-dispersible curable epoxy resins which would be distinguished by high stability in storage under practical storage conditions. A further problem addressed by the invention was to provide coating compositions containing a self-dispersible curable epoxy resin, the coating obtained from the coating composition after the curing process being distinguished by excellent properties.
It has now surprisingly been found that epoxy resins obtainable by reaction of xcex1,xcex2-unsaturated carboxylic acid esters with mono-, di- or polyaminopolyalkylene oxide compounds, subsequent reaction of the intermediate product obtained with an aromatic polyhydroxy compound and further reaction with an epoxy resin known from the prior art excellently satisfy the requirements mentioned in every respect.
The present invention relates first to self-dispersible curable epoxy resins obtainable by
(a) reacting one or more a,p-unsaturated carboxylic acid esters (I)
R2R3Cxe2x95x90C(R4)COOR1xe2x80x83xe2x80x83(I)
xe2x80x83where R1 is an aromatic or aliphatic radical containing up to 15 carbon atoms, the substituents R2, R3 and R4 independently of one another represent hydrogen, branched or unbranched, aliphatic or aromatic groups containing up to 20 carbon atoms or a group xe2x80x94(CH2)nxe2x80x94COOR1, where R1 is as defined above and n is a number of 0 to 10, with
(b) one or more mono-, di- or polyaminopolyalkylene oxide compounds, compounds (a) and (b) being used in such quantities that the equivalent ratio of the reactive hydrogen atoms at the aminonitrogen atoms of (b) to the Cxe2x95x90C double bond in the xcex1,xcex2-position to the group COOR1 shown in formula (I) in the carboxylic acid esters (a) is in the range from 10:1 to 1:10,
subsequently reacting the intermediate product Z1 obtained with
(c) one or more polyhydroxy compounds, the equivalent ratio of ester groups in the intermediate compound Z1 to hydroxy groups in the polyhydroxy compound (c) being adjusted to a value of 1:1.1 to 1-10,
and subsequently reacting the intermediate product Z2 obtained with
(d) one or more polyepoxides, the equivalent ratio of oxirane rings in polyepoxide (d) to hydroxyl groups in the intermediate product Z2 being adjusted to a value of 1.5:1 to 6:1.
The epoxy resins according to the invention are either liquid or solid substances, depending on their molecular weight.
The present invention also includes processes for the production of self-dispersing, hardenable epoxy resins.
The expression xe2x80x9cequivalent ratioxe2x80x9d is familiar to the expert. The basic concept behind the notion of the equivalent is that, for every substance participating in a reaction, the reactive groups involved in the desired reaction are taken into consideration. By indicating an equivalent ratio, it is possible to express the ratio which all the various reactive groups of the compounds (x) and (y) used bear to one another. It is important in this connection to bear in mind that a reactive group is understood to be the smallest possible reactive group, i.e. the notion of the reactive group is not identical with the notion of the functional group. In the case of H-acid compounds, this means for example that, although OH groups or NH groups represent such reactive groups, NH2 groups with two reactive H atoms positioned at the same nitrogen atom do not. In their case, the two hydrogen atoms within the functional group NH2 are appropriately regarded as reactive groups so that the functional group NH2 contains two reactive groups, namely the hydrogen atoms. Example: if a compound (a) containing one olefinic double bond in the xcex1,xcex2-position to a carboxyl group per molecule is reacted with a compound (b) containing one NH2 group per molecule by a Michael addition, compound (a) is regarded as containing one reactive group Cxe2x95x90C per molecule whereas compound (b) is regarded as containing two reactive hydrogen atoms attached to the nitrogen. If, now, (a) and (b) were to be reacted in an equivalent ratio of 1:1, one mole of (a) would have to be reacted with half a mole of (b) because (b) does of course contain two reactive groups per molecule. By contrast, for an equivalent ratio of (a) to (b) of 1:2, 1 mole of (a) would have to be reacted with 1 mole of (b). An equivalent ratio of, for example, (a) to (b) of 1:10 could of course also be adjusted although in that case 1 mole of (a) would have to be reacted with 5 moles of (b). This would mean that component (b) would be used in excess because, of course, at most 1 mole of component (b) could theoretically be reacted with (a) in a Michael addition.
So far as the compounds belonging to classes (a) to (c) are concerned, it is expressly pointed out that they are different substances.
In one embodiment, compounds (a) and (b) are used in such quantities that the equivalent ratio of reactive hydrogen atoms at the aminonitrogen atoms of (b) to the Cxe2x95x90C double bond in the xcex1,xcex2-position to the group COOR1 in formula (I) in the carboxylic acid esters (a) is in the range from 4:1 to 1:4 and more particularly in the range from 2.5:1 to 1.5:1.
In another embodiment, the equivalent ratio of ester groups in intermediate compound Z1 to hydroxy groups in polyhydroxy compound (c) is adjusted to a value of 1:1.4 to 1:3.
In another embodiment, the equivalent ratio of oxirane rings in the polyepoxide (d) to hydroxyl groups in intermediate product Z2 is adjusted to a value in the range from 2.5:1 to 3.5:1.
Examples of the xcex1,xcex2-unsaturated carboxylic acid esters (a) corresponding to formula (I) to be used in accordance with the invention are methyl acrylate, ethyl acrylate, dimethyl maleate, diethyl maleate, dimethyl fumarate, diethyl fumarate, dimethyl itaconate, diethyl itaconate. Particularly preferred compounds (a) are dialkyl maleates, more particularly diethyl maleate and dimethyl maleate.
Suitable amino components (b) are mono-, di- or polyaminopolyalkylene oxide compounds. By this is meant that these compounds contain on the one hand one, two or more amino functions (NH or NH2 functions) and, on the other hand, alkylene oxide units. The alkylene oxide units are, in particular, ethylene oxide, propylene oxide and butylene oxide, ethylene oxide and propylene oxide being particularly preferred. The compounds (b) are substances at least partly soluble in water at 20xc2x0 C.
The production of the compounds (b) is known from the prior art and comprises the reaction of hydroxyfunctional compounds with alkylene oxides and subsequent conversion of the resulting terminal hydroxyl groups into amino groups.
So far as the reaction of hydroxyfunctional compounds with alkylene oxides is concerned, ethoxylation and propoxylation are of particular importance. The following procedure is usually adopted: in a first step, the required hydroxyfunctional compounds are contacted with ethylene oxide and/or propylene oxide and the resulting mixture is reacted in the presence of an alkaline catalyst at temperatures in the range from 20 to 200xc2x0 C. Addition products of ethylene oxide (EO) and/or propylene oxide (PO) are obtained in this way. The addition products are preferably EO adducts or PO adducts or EO/PO adducts with the particular hydroxyfunctional compound. In the case of the EO/PO adducts, the addition of EO and PO may be carried out statistically or blockwise.
In one embodiment, substances with the general formula R8xe2x80x94Oxe2x80x94R9xe2x80x94CH2CH(R10)xe2x80x94NH2 are used as the compounds (b). In this formula:
R8 is a monofunctional organic group containing 1 to 12 carbon atoms which may be aliphatic, cycloaliphatic or aromatic,
R9 is a polyoxyalkylene group made up of 5 to 200 polyoxyalkylene units, more particularly EO and/or PO units,
R10 is hydrogen or an aliphatic radical containing up to 4 carbon atoms.
Particularly suitable representatives of the compounds (b) for the purposes of the present invention are the xe2x80x9cJeffaminesxe2x80x9d known to the expert which are commercially available substances. One example is xe2x80x9cJeffamine 2070xe2x80x9d which, according to the manufacturer Texaco, is produced by reacting methanol with ethylene oxide and propylene oxide and then converting the terminal hydroxyl groups of the intermediate product initially obtained into amine groups (cf. WO 96/20971, page 10, lines 12-15).
The compounds (b) preferably have average molecular weights (number average Mn) of 148 to 5,000 and more particularly in the range from 400 to 2,000.
The polyhydroxy compounds (c) may be aliphatic or aromatic.
In one embodiment, the polyols (c) are selected from the class of special aliphatic diols, namely alkanediols, polyetherdiols and polyester diols.
The alkanediols are compounds corresponding to the general formula HOCH2xe2x80x94R5xe2x80x94CH2OH, where R5 is a hydrophobic hydrocarbon radical which may be saturated or unsaturated, linear or branched and may also contain aromatic structural elements. Examples are hexane-1,6-diol, heptane-1,7-diol and octane-1,8-diol, polyoxytetramethylenediolsxe2x80x94also known as polytetrahydrofuransxe2x80x94and the so-called dimerdiols.
Dimerdiols are well-known commercially available compounds which are obtained, for example, by reduction of dimer fatty acid esters. The dimer fatty acids on which these dimer fatty acid esters are based are carboxylic acids which may be obtained by oligomerization of unsaturated carboxylic acids, generally fatty acids, such as oleic acid, linoleic acid, erucic acid and the like. The oligomerization is normally carried out at elevated temperature in the presence of a catalyst, for example of alumina. The substances obtainedxe2x80x94dimer fatty acid of technical qualityxe2x80x94are mixtures in which the dimerization products predominate. However, small amounts of higher oligomers, more particularly the trimer fatty acids, are also present. Dimer fatty acids are commercially available products and are marketed in various compositions and qualities. Abundant literature is available on the subject of dimer fatty acids, cf. for example the following articles: Fefte and xc3x96le 26 (1994), pages 47-51; Speciality Chemicals 1984 (May Number), pages 17, 18, 22-24. Dimerdiols are well-known among experts, cf. for example a more recent article in which inter alia the production, structure and chemistry of the dimerdiols are discussed: Fat Sci. Technol. 95 (1993), No. 3, pages 91-94. According to the invention, preferred dimerdiols are those which have a dimer content of at least 50% and more particularly 75% and in which the number of carbon atoms per dimer molecule is mainly in the range from 36 to 44.
Polyetherdiols in the context of the present invention are diols corresponding to the general formula HOCH2xe2x80x94R6xe2x80x94CH2OH, where R6 is a hydrophobic hydrocarbon radical which may be saturated or unsaturated, linear or branched and may also contain aromatic structural elements and in which one or more CH2 units must each be replaced by an oxygen atom.
A particularly attractive class of polyetherdiols can be obtained by alkoxylation of alkanediols, such as ethane-1,2-diol, propane-1,3-diol, propane-1,2-diol, butane-1,4-diol, butane-1,3-diol, pentane-1,5-diol, hexane-1,6-diol, heptane-1,7-diol and octane-1,8-diol, polyoxytetra-methylenediols (polytetrahydrofurans) and dimerdiols. The production of these alkoxylated diols is normally carried out as follows: in a first step, the required diol is contacted with ethylene oxide and/or propylene oxide and the resulting mixture is reacted in the presence of an alkaline catalyst at temperatures of 20 to 200xc2x0 C. Addition products of ethylene oxide (EO) and/or propylene oxide (PO) onto the diol used are obtained in this way. The addition products are therefore EO adducts or PO adducts or EO/PO adducts with the particular diol; in the case of the EO/PO adducts, the addition of EO and PO may take place statistically or blockwise.
Polyesterdiols in the context of the invention are diols corresponding to the general formula HOCH2xe2x80x94R7xe2x80x94CH2OH, where R7 is a hydrophobic hydrocarbon radical which may be saturated or unsaturated, linear or branched and may also contain aromatic structural elements and in which one or more CH2 units must each be replaced by a COO unit. They are normally produced by reacting difunctional polyols with dicarboxylic acids or anhydrides thereof. Commonly used polyols are ethylene glycol, propane-1,2-diol, butane-1,4-diol, hexane-1,6-diol. Typical dicarboxylic acids are succinic acid, adipic acid, phthalic anhydride. Hexane-1,6-diol adipic acid polyesters are particularly preferred.
Examples of suitable aromatic compounds (c) are resorcinol, hydroquinone, 2,2-bis-(4-hydroxyphenyl)-propane (bisphenol A), isomer mixtures of dihydroxydiphenyl methane (bisphenol F), tetrabromobisphenol A, 4,4xe2x80x2-dihydroxydiphenyl cyclohexane, 4,4xe2x80x2-dihydroxy-3,3-dimethyldiphenyl propane, 4,4xe2x80x2-dihydroxydiphenyl, 4,4xe2x80x2-dihydroxybenzopenol, bis-(4-hydroxyphenyl)-1,1 -ethane, bis-(4-hydroxyphenyl)-1,1 -isobutane, bis-(4-hydroxyphenyl)-methane, bis-(4-hydroxyphenyl(-ether, bis-(4-hydroxyphenyl)-sulfone etc. and the chlorination and bromination products of the above-mentioned compounds. Bisphenol A is most particularly preferred as compound (c). 
The epoxy compounds (d) are polyepoxides containing on average at least two epoxy groups per molecule. These epoxy compounds may be both saturated and unsaturated and aliphatic, cycloaliphatic, aromatic and heterocyclic and may also contain hydroxyl groups. They may also contain substituents which do not cause any troublesome secondary reactions under the mixing and reaction conditions, for example alkyl or aryl substituents, ether groups and the like. These epoxy compounds are preferably polyglycidyl ethers based on polyhydric, preferably dihydric alcohols, phenols, hydrogenation products of these phenols and/or novolaks (reaction products of mono- or polyhydric phenols with aldehydes, more particularly formaldehyde, in the presence of acidic catalysts). The epoxy equivalent weights of these epoxy compounds are preferably between 160 and 500 and more preferably between 170 and 250. The epoxy equivalent weight of a substance is the quantity of the substance (in grams) which contains 1 mole of oxirane rings.
Preferred polyhydric phenols are the compounds described under (c). The polyglycidyl ethers of polyhydric alcohols are also suitable. Examples of such polyhydric alcohols are ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, polyoxypropylene glycols (nxe2x95x901-20), 1,3-propylene glycol, 1,4-butylene glycol, pentane-1,5-diol, hexane-1,6-diol, hexane-1,2,6-triol, glycerol and bis-(4-hydroxycyclohexyl)-2,2-propane.
Other suitable compounds (d) are polyglycidyl ethers of polycarboxylic acids obtained by reaction of epichlorohydrin or similar epoxy compounds with an aliphatic, cycloaliphatic or aromatic polycarboxylic acid, such as oxalic acid, succinic acid, adipic acid, glutaric acid, phthalic acid, terephthalic acid, hexahydrophthalic acid, 2,6-naphthalenedicarboxylic acid and dimerized linolenic acid. Examples are adipic acid diglycidyl ester, phthalic acid diglycidyl ester and hexahydrophthalic acid diglycidyl ester. A comprehensive list of suitable epoxy compounds (d) can be found in:
A.M. Paquin, xe2x80x9cEpoxidverbindungen und Epoxidharzexe2x80x9d, Springer-Verlag, Berlin 1958, Chapter V, pages 308 to 461 and
Lee, Neville xe2x80x9cHandbook of Epoxy Resinsxe2x80x9d 1967, Chapter 2, pages 201 and 2-33.
Mixtures of several epoxy compounds (d) may also be used.
The present invention also relates to a process for the production of self-dispersible curable epoxy resins comprising the steps of
(a) reacting one or more xcex1,xcex2-unsaturated carboxylic acid esters (I)
xe2x80x83R2R3Cxe2x95x90C(R4)COOR1xe2x80x83xe2x80x83(I)
xe2x80x83where R1 is an aromatic or aliphatic radical containing up to 15 carbon atoms, the substituents R2, R3 and R4 independently of one another represent hydrogen, branched or unbranched, aliphatic or aromatic groups containing up to 20 carbon atoms or a group xe2x80x94(CH2)nxe2x80x94COOR1, where R1 is as defined above and n is a number of 0 to 10, with
(b) one or more mono-, di- or polyaminopolyalkylene oxide compounds, compounds (a) and (b) being used in such quantities that the equivalent ratio of the reactive hydrogen atoms at the aminonitrogen atoms of (b) to the Cxe2x95x90C double bond in the xcex1,xcex2-position to the group COOR1 shown in formula (I) in the carboxylic acid esters (a) is in the range from 10:1 to 1:10,
subsequently reacting the intermediate product Z1 obtained with
(c) one or more polyhydroxy compounds, the equivalent ratio of ester groups in the intermediate compound Z1 to hydroxy groups in the polyhydroxy compound (c) being adjusted to a value of 1:1.1 to 1-10,
and subsequently reacting the intermediate product Z2 obtained with
(d) one or more polyepoxides, the equivalent ratio of oxirane rings in polyepoxide (d) to hydroxyl groups in the intermediate product Z2 being adjusted to a value of 1.5:1 to 6:1.
The present invention also relates to aqueous dispersions containing the self-dispersible curable epoxy resins according to the invention. The content of the epoxy resins according to the invention in these dispersions is between 40 and 70% by weight, based on the dispersion as a whole.
In many cases, aqueous dispersions containing the epoxy resins obtainable by the process according to the invention are distinguished by very small mean particle sizes of around 500 nm or smaller. This leads to very favorable material properties of the coatings formed with these dispersions. Particularly favorable material properties are obtained when the mean particle size is below about 300 nm. The mean particle size is defined as the average of the particle sizes which is obtained by adding the values of n individual measurements and then dividing the total by n. For the purposes of the present invention, the mean particle sizes were determined using a xe2x80x9cCoulter N4 Plus Submicron Particle Sizerxe2x80x9d (manufacturer: Coulter, Miami, Fla. 33196, USA). This instrument uses the scattering of laser light at a heavily diluted dispersion for particle size determination. It performs a number of individual measurements and gives the mean particle size as the end result. The above-mentioned values relate to scattering measurements at an angle of 90xc2x0 relative to the incident laser beam.
The self-dispersible curable epoxy resins according to the invention are suitable in combination with suitable hardeners, more particularly the amine hardeners known to the relevant expert, and optionally other typical additives for the production of coatings, intermediate coatings, paints, molding compositions and curable pastes for various applications. For example, they may be used for the production of protective and/or decorative coatings on various, above all rough and porous substrates such as, for example, wood, mineral substrates (for example concrete and stone), glass, plastics (for example polyethylene, polypropylene), compost materials, ceramics and pretreated or non-pretreated metals. Their favorable properties also make the epoxy resins according to the invention eminently suitable for one-coat lacquering/painting. The adhering coating layer may remain unchanged as such although it may also serve as an intermediate layer, i.e. as a substrate for further coatings which in turn may consist of the same coating material or of another typical coating material.
Accordingly, the present invention also relates to the use of the self-dispersible curable epoxy resins according to the invention for the applications mentioned.
Aqueous dispersions containing the epoxy resins according to the invention are distinguished by good dilutability and favorable performance properties. Apart from the applications already mentioned, they are also suitable for use in electrodeposition painting. In addition, aqueous dispersions containing the epoxy resins according to the invention may also be used for the production of water-dilutable adhesives, as binders for textile, organic and/or inorganic materials and as an additive in plastic cements.